1. Field of the Invention
The present invention relates to reciprocating piston compressors, and more particularly, to reciprocating piston compressors having an improved piston design and a vented cylinder.
2. Description of the Related Art
Conventional reciprocating compressors commonly include a hermetically sealed housing defining an interior plenum. The housing includes a suction inlet and a discharge outlet, through which a compressible fluid respectively enters and exits the compressor assembly. A motor is generally disposed in the interior plenum to rotationally drive a shaft. The shaft typically includes a journal that defines an axis offset from the rotational axis of the shaft thereby causing the journal to travel through a circular arc centered on the rotational axis of the shaft. A cylinder block will also generally be disposed in the interior plenum and define a compression cylinder having a single diameter. A substantially cylindrical piston having a single diameter is disposed within the cylinder. A wrist pin is often used to connect the piston with a piston rod. The piston rod is also secured to the journal whereby the rotational motion of the shaft is converted to reciprocating movement of the piston along the axis of the compression cylinder. The compressible fluid is drawn into the cylinder and compressed by the reciprocation of the piston within the cylinder.
Converting the rotational movement of the shaft into the reciprocating movement of the piston generates side loads that are transverse to both the rotational axis of the shaft and to the axis of the cylinder. These side loads typically result in a portion of the piston bearing against the sidewall of the cylinder. Normal operation of the compressor may also result in a relatively large load being placed on the wrist pin that connects the piston rod with the piston. When using a refrigerant that must be compressed to a relatively high pressure, such as carbon dioxide, these loads can become significant and may, thereby, adversely affect the performance and durability of a conventional reciprocating compressor design.